The present invention relates to tertiary amine catalysts for producing rigid polyurethane foam.
Polyurethane foams are widely known and used in automotive, housing and other industries. Such foams are produced by reaction of a polyisocyanate with a polyol in the presence of various additives. One such additive is a chlorofluorocarbon (CFC) blowing agent which vaporizes as a result of the reaction exotherm, causing the polymerizing mass to form a foam. CFCs were of value in insulating rigid foams due to their low thermal conductivity as measured by their k-factors.
The discovery that CFCs deplete ozone in the stratosphere has resulted in mandates diminishing CFC use. Production of water-blown foams, in which blowing is performed with CO2 generated by the reaction of water with the polyisocyanate, has therefore become increasingly important.
Tertiary amine catalysts are typically used to accelerate blowing (reaction of water with isocyanate to generate CO2) and gelling (reaction of polyol with isocyanate). The ability of the tertiary amine catalyst to selectively promote either blowing or gelling is an important consideration in selecting a catalyst for the production of a particular polyurethane foam. If a catalyst promotes the blowing reaction to a too high degree, much of the CO2 will be evolved before sufficient reaction of isocyanate with polyol has occurred, and the CO2 will bubble out of the formulation, resulting in collapse of the foam. A foam of poor quality will be produced. In contrast, if a catalyst too strongly promotes the gelling reaction, a substantial portion of the CO2 will be evolved after a significant degree of polymerization has occurred. Again, a poor quality foam, this time characterized by high density, broken or poorly defined cells, or other undesirable features, will be produced.
Tertiary amine catalysts generally are malodorous and offensive and many have high volatility due to their low molecular weight. Release of tertiary amines during foam processing may present significant safety and toxicity problems, and release of residual amines from consumer products is generally undesirable.
Amine catalysts which contain urea functionality (e.g., RNHCONHR') have an increase in molecular weight and hydrogen bonding and, therefore, reduced volatility and odor when compared to related structures which lack this functionality. Furthermore, catalysts which contain urea functionality chemically bond into the urethane during the reaction and are not released from the finished product. Catalyst structures which embody this concept are typically of low to moderate activity and promote both the blowing (water-isocyanate) and the gelling (polyol-isocyanate) reactions to varying extents.
U.S. Pat. No. 5,859,079 discloses a polyurethane catalyst composition for making flexible polyurethane foam comprising N,N'-bis(3-dimethylaminopropyl) urea and 3-dimethylaminopropyl urea in a ratio that can be varied to systematically control flowability, airflow and force-to-crush physical properties of the resulting flexible foam.
U.S. Pat. No. 4,644,017 discloses the use of certain diffusion stable amino alkyl ureas having tertiary amino groups in the production of a polyisocyanate addition product which do not discolor or change the constitution of surrounding materials. Specifically taught are Catalyst A and Catalyst D which are reaction products of dimethylamino-propylamine and urea.
U.S. Pat. No. 4,007,140 discloses the use of N,N'-bis(3-dimethylaminopropyl)urea as a low odor catalyst for the manufacture of polyurethanes.
U.S. Pat. No. 4,194,069 discloses the use of N-(3-dimethylaminopropyl)-N'-(3-morpholinopropyl)urea, N,N'-bis(3-dimethylaminopropyl)urea and N,N'-bis(3-morpholinopropyl)urea as catalysts for producing polyurethane foams.
U.S. Pat. No. 4,094,827 discloses the use of certain alkyl substituted ureas including N,N-bis(3-dimethylaminopropyl)urea which provide lower odor and a delay in the foaming reaction that aids in the production of polyurethane foam.
U.S. Pat. No. 4,330,656 discloses the use of N-alkyl ureas as catalysts for the reaction of 1,5-napthylene diisocyanate with polyols or for the chain extension of prepolymers based upon 1,5-napthylene diisocyanate without accelerating atmospheric oxidation.
DE 30 27 796 A1 discloses the use of higher molecular weight dialkyl aminoalkyl ureas as reduced odor catalysts for the production of polyurethane foam.
U.S. Pat. No. 4,310,632 and U.S. Pat. No. 5,057,480 disclose a process for making polyurethane using a defined catalyst.